There has been known a technique that, by performing so-called EGR which introduces exhaust gas into an intake system in accordance with an operating condition, improves exhaust performance and increases fuel economy of an internal combustion engine.
For instance, Patent Document 1 discloses a technique that, even during execution of the EGR, controls an opening degree of a nozzle vane of a variable displacement turbocharger so that an actual boost pressure becomes a target boost pressure that is calculated on the basis of an engine speed and an engine load.
In such a technique of Patent Document 1, however, although a steady torque demand can be satisfied when introducing the EGR from an upstream side with respect to a compressor housing of the turbocharger, there is a risk that a torque step caused by a transient change of a quantity of intake air in a cylinder which occurs upon start and stop of the EGR can not be avoided.